In the processing of binders based on calcium sulfate, setting accelerating additives or setting accelerators are often used. In this way, the setting times of the binders can be greatly reduced, which is of decisive advantage, for example, in the major industrial production of plasterboard.
An effective setting accelerator for binders based on calcium sulfate is finely ground gypsum or calcium sulfate dihydrate (CaSO4.2 H2O). Gypsum acts here for example as a seed crystal, which accelerates the hydration of the calcium sulfate hemihydrate and/or anhydrite present in the binder.
During the production of such setting accelerators, additives are often added to the gypsum during the production, such as starch, sugar or dextrin. These additives serve, for example, to promote the grinding process of the gypsum or to influence the properties of the gypsum after the grinding. For example, additives facilitate the fragmentation of the gypsum in the grinding mills and prevent an agglomeration of the resulting fine particles. Other additives instead increase the setting accelerating action or stability of the gypsum after the grinding.
U.S. Pat. No. 4,298,394 describes in this context, for example, the use of up to 20 wt. % of a surfactant substance as an additive during the grinding of gypsum. Specifically mentioned are, e.g., sodium alkylate sulfonate, sodium lauryl sulfate or ethoxylated nonyl phenol. The use of these additives provides, for example, an improved storage stability and increased setting acceleration.
But many additives and production methods for setting accelerators based on gypsum are not entirely effective. Often they improve only the grinding process or the gypsum properties, for example, the setting accelerating action. Thus, an improvement in the area of the grinding process works to the disadvantage of the setting accelerating action and vice versa. Other methods and additives have economic drawbacks or are expensive in technical implementation.